Turbomachines are widely utilized in fields such as power generation. For example, a conventional gas turbine system includes a compressor section, a combustor section, and at least one turbine section. The compressor section is configured to compress air as the air flows through the compressor section. The air is then flowed from the compressor section to the combustor section, where it is mixed with fuel and combusted, generating a hot gas flow. The hot gas flow is provided to the turbine section, which utilizes the hot gas flow by extracting energy from it to power the compressor, an electrical generator, and other various loads.
The turbine section typically includes multiple stages which are disposed along the hot gas path such that the hot gases flow through first-stage nozzles and rotor blades and through the nozzles and rotor blades of follow-on turbine stages. The turbine rotor blades may be secured to a plurality of rotor disks comprising the turbine rotor, with each rotor disk being mounted to the rotor shaft for rotation therewith.
A turbine rotor blade generally includes an airfoil extending radially outwardly from a substantially planar platform and a shank portion extending radially inwardly from the platform for securing the rotor blade to one of the rotor disks. The tip of the airfoil is typically spaced radially inwardly from a stationary shroud of the turbomachine such that a small gap is defined between the tip and the shroud. This gap is typically sized as small as practical to minimize the flow of hot gases between the airfoil tip and the shroud.
In many instances, the tip of the airfoil may include a squealer tip wall extending around the perimeter of the airfoil so as to define a tip cavity and a tip floor therebetween. The squealer tip wall is generally used to reduce the size of the gap defined between the airfoil tip and the shroud. However, this creates an additional component of the turbine rotor blade that is subject to heating by the hot gas flowing around the airfoil. Thus, cooling holes are typically defined in the tip floor to allow a cooling medium to be directed from an airfoil cooling circuit within the airfoil to the tip cavity. Although the squealer tip wall reduces the size of the gap defined between the airfoil tip and the shroud, some over tip leakage can roll over the tip wall. Such flows may result in formation of a strong vortex flow on the suction side of the blade surface, which leads to entropy generation and loss in performance.